Manufacturing method for field-effect transistor

ABSTRACT

To provide a manufacturing method for a field-effect transistor, such as a thin-film transistor, enabling reductions in the number patterning steps and the number of photomasks and improvements in the throughput and the yield. In the method, an oxide film is formed by processing the surface of a crystalline semiconductor with ozone water or hydrogen peroxide water. Using the oxide film thus formed as an etch stop, a gate electrode, a source electrode, and a drain electrode of the field-effect transistor are simultaneously formed from a same starting film in one patterning step by use of one photomask. After forming the gate electrode, the source electrode, and the drain electrode, heating is performed thereon at 800° C. or higher for a predetermined time. Thereby, the contact resistances between the source electrode and the crystalline semiconductor and between the drain electrode and the crystalline semiconductor are reduced, whereby improving the electrical conductivity.

This application is a divisional of U.S. application Ser. No.11/646,688, filed on Dec. 28, 2006 now U.S. Pat. No. 7,718,478 which isa divisional of U.S. application Ser. No. 10/844,143, filed on May, 12,2004 (now U.S. Pat. No. 7,157,317 issued Jan. 2, 2007) which is adivisional of U.S. application Ser. No. 10/284,275 filed on Oct. 30,2002 (now U.S. Pat. No. 6,737,302 issued May 18, 2004).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a field-effect transistor such as athin-film transistor and to a manufacturing method therefor. Further,the present invention relates to a manufacturing method for a displaydevice using the field-effect transistors and to a display devicemanufactured using the manufacturing method for the display device. Morespecifically, the present invention relates to a field-effect transistorsuch as a thin-film transistor having a gate electrode, a sourceelectrode, and a drain electrode, of the thin-film transistorsimultaneously formed by patterning a same starting film by use ofphotolithography and to a manufacturing method therefor.

2. Description of the Related Art

Hereinbelow, an example of a conventional manufacturing procedure for athin-film transistor will be described. An amorphous silicon film isformed on the upper side of a glass substrate, the amorphous siliconfilm is crystallized, and a crystalline silicon film is thereby formed.Then, the crystalline silicon film is patterned into an island-likecrystalline silicon film, and a gate insulation film is formed on theisland-like crystalline silicon film. Subsequently, a conductive filmformed on the gate insulation film is patterned, and a gate electrode isthereby formed. Then, using the gate electrode as a mask, an impurity isintroduced to the island-like crystalline silicon film by using an iondoping method, and a source region and a drain region are therebyformed. Next, a first interlayer insulation film is formed on both thegate electrode and the island-like crystalline silicon film. Then, anopening (contact hole) is formed by performing patterning on the firstinterlayer insulation film so as to reach the source region and thedrain region. Thereafter, a conductive film to be connected to thesource region and the drain region is formed, and the conductive film isthen patterned. Thereby, a source electrode and a drain electrode areformed. The thin-film transistor is manufactured according to theabove-described procedure. The aforementioned procedure is well known(Refer to, for example, a patent document 1 below). When applying thethin-film transistor manufactured according to the well-known art to apixel portion of a display device, a second interlayer insulation filmis formed on both the source electrode and the drain electrode, and anopening is formed by performing patterning so as to reach one of thesource electrode and the source electrode. In addition, a transparentconductive film is formed and patterned, and a pixel electrode is thenformed.

(Patent Document 1)

Japanese Patent Application Laid-open No. Hei 8-330602 (FIGS. 1A to 1F;First Embodiment)

As described above, according to the conventional procedure, the sourceelectrode and the drain electrode are formed after the gate electrodehas been formed. That is, ordinarily, formation of the gate electrodeand formation of the source electrode and the drain electrode areseparately performed. Therefore, in the processes progressed to thestage where the formation of the source electrode and the drainelectrode is completed, four patterning steps are performed, and fourphotomasks are used in the patterning steps. To complete the formationof the pixel electrode, two more patterning steps are performed. Thatis, in the above case, the number of the patterning steps is six, andthe number of the photomasks used in the patterning steps is accordinglysix.

At present, improvements in the throughput (quantity that can beprocessed in a unit time) and the yield (ratio of the number of finishedproducts to the number of inputs to a manufacturing line) are stronglydemanded in the field of the manufacture of field-effect transistorssuch as thin-film transistors and display devices using the field-effecttransistors.

However, in the conventional procedure, since the number of steps in theconventional procedure is large, the time required for the manufactureof field-effect transistors and display devices cannot easily bereduced, and it is difficult to improve the yield. For example, becauseof shrinkage of a substrate or for other causes, a positional offset ofa fine pattern formed in a subsequent patterning step can unexpectedlyoccur. The positional offset of the pattern results in the manufactureof defective products as well as in reduction in the yield. For example,in a step of forming an opening (contact hole) by performing patterningto form the source electrode and the drain electrode, the position ofthe opening is offset from the source region and the drain region wherethe opening is intended to be provided.

A case can be in which even when a positional offset of a pattern iscaused at one patterning step, the offset is as slight as that fallingwithin an allowable tolerance, and no adverse effects are thereby causedon the operation of a finished display device. However, when a number ofpatterning steps are repeatedly performed, the slight positional offsetis enlarged, thereby increasing the probability of defective-productoccurrence.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and an objectof the present invention is therefore to improve the yield by reducingthe number of patterning steps and to reduce the manufacturing time byreducing the number of photomasks and by reducing the number ofpatterning steps in a way that incorporates a plurality of steps intoone step.

According to the present invention, a surface of a crystallinesemiconductor is oxidized using an oxidizing water solution, such asozone water solution or hydrogen peroxide water solution, and an oxidefilm is thereby formed. With the oxide film being used as an etch stop,the gate electrode, the source electrode, and the drain electrode of afield-effect transistor are simultaneously formed from a same startingfilm. After the gate electrode, the source electrode, and the drainelectrode have been formed, the electrodes are heated at a temperatureof 800° C. or higher for a predetermined time in an ambient of an inertgas. In this case, either an argon gas or a nitrogen gas is used as theinert gas.

Further, according to the present invention, there is provided amanufacturing method for a field-effect transistor, comprising: forminga first insulation film on a crystalline semiconductor; forming a gateinsulation film on a portion of the crystalline semiconductor bypatterning the first insulation film; forming an oxide film by oxidizinga surface of the crystalline semiconductor by using an oxidizing watersolution, such as ozone water solution or hydrogen peroxide watersolution; forming a conductive film on the oxide film and the gateinsulation film, the conductive film comprising a semiconductor filmcontaining an n-type impurity; simultaneously forming a gate electrode,a source electrode, a drain electrode by patterning the conductive film;and introducing an n-type impurity to the crystalline semiconductor byusing the gate electrode, the source electrode, and the drain electrodeas masks. In the above stage, the oxide film exists between the sourceelectrode and the crystalline semiconductor, and between the drainelectrode and the crystalline semiconductor, the oxide film containingSiO_(x) (0<X<2) and SiO₂. Thereafter, the crystalline semiconductor, theoxide film, the gate insulation film, the gate electrode, the sourceelectrode, and the drain electrode are heated in an inert gas ambient,for example, a nitrogen ambient, at a temperature of from 800° C. to1050° C. for a time period of from 30 minutes to 4 hours. By theheating, the n-type impurity contained in each of the source electrodeand the drain electrode can be dispersed to the crystallinesemiconductor, and in addition, the n-type impurity can be activated.Concurrently, the heating works to reduce the contact resistance betweenthe source electrode and the crystalline semiconductor and the contactresistance between the drain electrode and the crystallinesemiconductor. Instead of using the semiconductor film containing then-type impurity, a semiconductor film containing a p-type impurity maybe used; and instead of introducing the n-type impurity to thecrystalline semiconductor, the p-type impurity may be introducedthereto.

According to the present invention, the oxide film, which has beenformed such that the surface of the crystalline semiconductor isoxidized using one of the oxidizing water solution such as ozone watersolution or hydrogen peroxide water solution, operates as an etch stopat the time of simultaneously forming the gate electrode, the sourceelectrode, and the drain electrode from the conductive film. Therefore,the crystalline semiconductor is remained unetched. Ozone and hydrogenperoxide used to form the oxide film are water-soluble and each known asan oxidizer that oxidizes other materials. The conductive film needs tobe formed using a material having a melting point higher than thetemperature set in the above-described heating. In addition, theconductive film may be formed by overlaying metal having a melting pointof 800° C. or higher on the crystalline silicon containing the n-typeimpurity. The metal may be selected from, for example, copper,palladium, chromium, cobalt, titanium, molybdenum, niobium, tantalum,and tungsten. Alternatively, the metal may be selected from metalsilicide substrates such as cobalt silicide, titanium silicide,molybdenum silicide, niobium silicide, tantalum silicide, and tungstensilicide. Still alternatively, the conductive film may be formed incombination with a metal nitride substance, such as titanium nitride,tantalum nitride, or tungsten nitride.

In the present invention, the crystalline semiconductor is one ofmonocrystalline and polycrystalline semiconductors and is not limited tothe form of a thin film. When using the crystalline semiconductor in theform of a thin film, a semiconductor film may be formed on the upperside of the substrate, and a crystalline semiconductor film formed bycrystallizing the semiconductor film may be used. According to thepresent invention, since the heat treatment is performed at atemperature of from 800° C. to 1050° C., a usable substrate is limitedto a substrate, such as a quartz substrate, a silicon substrate, or astainless steel substrate, which is not deformable because of the heattreatment.

The present invention enables the use of such a method as describedhereunder. Before forming a conductive film for the use of forming agate electrode, a source electrode, and a drain electrode, the n-typeimpurity is introduced to a crystalline semiconductor by using the gateinsulation film. Then, the gate electrode, the source electrode, and thedrain electrode are formed. Thereafter, the n-type impurity isintroduced again to the crystalline semiconductor, and a heat treatmentis performed at a temperature of from 800° C. to 1050° C. In this case,a p-type impurity may be introduced to the semiconductor instead of then-type impurity. In addition, as a material for forming the conductivefilm, a semiconductor including the n-type impurity or the p-typeimpurity need not always be used.

The above-described manufacturing method for a field-effect transistormay be applied to the manufacture of a display device using field-effecttransistors manufactured according to the manufacturing method. Examplesof the display device include an active matrix liquid crystal displaydevice and an active matrix display device using light emitting devices(LEDs).

According to another aspect of the present invention, a field-effecttransistor manufactured by using the manufacturing method for afield-effect transistor includes an island-like crystallinesemiconductor film on the upper side of a substrate, a gate insulationfilm formed in a portion of the island-like crystalline semiconductorfilm, a source electrode and a drain electrode formed on the island-likecrystalline semiconductor film, and a gate electrode formed on the gateinsulation film, wherein the island-like crystalline semiconductor filmincludes a source region, a drain region, a low-density impurity region(LDD region), and a channel region; and SiO_(x) (0<X<2) between thesource electrode and source region and between the drain electrode andthe drain region.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1E are cross-sectional views illustrative of a firstembodiment mode according to the present invention;

FIGS. 2A to 2E are cross-sectional views illustrative of the firstembodiment mode according to the present invention;

FIGS. 3A to 3E are cross-sectional views illustrative of a secondembodiment mode according to the present invention;

FIGS. 4A to 4C are cross-sectional views illustrative of a fourthembodiment mode according to the present invention;

FIGS. 5A to 5E are cross-sectional views illustrative of a first exampleaccording to the present invention;

FIGS. 6A to 6D are cross-sectional views illustrative of the firstexample according to the present invention;

FIGS. 7A to 7C are cross-sectional views illustrative of the firstexample according to the present invention;

FIGS. 8A to 8D are cross-sectional views illustrative of a secondexample according to the present invention;

FIG. 9 is a cross-sectional view of a third example according to thepresent invention; and

FIG. 10A is a cross-sectional view of a transistor and FIG. 10B is achart showing effects of heat treatments according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(First Embodiment Mode)

Hereinbelow, a first embodiment mode will be described using FIGS. 1A to1E, 2A to 2E, 10A, and 10B.

As shown in FIG. 1A, a first insulation film 102 is formed on asubstrate 101 in a range of from 100 nm to 1000 nm. The first insulationfilm 102 may be any one of a silicon oxynitride film formed using a CVDmethod in which SiH₄ and N₂O are used as source materials, a siliconnitride oxide film formed using the CVD (chemical vapor deposition)method in which SiH₄, N₂O, and NH₃ are used as source materials, asilicon oxide film, a nitrogen-containing silicon oxide film, and asilicon nitride film. Alternatively, the first insulation film 102 maybe formed by combining and overlaying two or more of the aforementionedfilms. For the substrate 101, one of a quartz substrate, a siliconsubstrate, and a stainless steel substrate is used. When the quartzsubstrate is used, the first insulation film 102 need not be formed.

Subsequently, a semiconductor film 103 with a thickness of from 30 nm to80 nm is formed on one of the substrate 101 and the first insulationfilm 102. The semiconductor film 103 may be any one of a silicon film, agermanium film, and a film containing silicon and germanium. The lessthe thickness of a semiconductor film in a range of from 30 nm to 80 nm,the greater the effects of reducing off-state current of a thin-filmtransistor.

Next, the semiconductor film 103 is crystallized using a well-knownmethod. The semiconductor film 103 may be crystallized using any one ofsolid-phase epitaxy in which heat treatments are performed using anelectric furnace, laser crystallization in which gas-laser orsolid-state laser light of pulse oscillations or continuous oscillationsis irradiated, and RTA (rapid thermal annealing). In solid-phaseepitaxy, a method of doping the semiconductor film 103 with an elementsuch as nickel for accelerating crystallization of a semiconductor filmmay be used. However, while the method is effective since it enables tolower the heating temperature and to reduce the heating time, the nickelcontained in the semiconductor film 103 needs to be gettered and removedas much as possible after crystallization.

At present, as a method of crystallizing semiconductor films, lasercrystallization is widely researched. Hereinbelow, lasers to be used forthe crystallization will be described in detail.

Gas lasers that may be used include, for example, an excimer laser, anAr laser, and a Kr laser. Solid-state lasers that may be used include,for example, a YAG laser, a glass laser, a ruby laser, an alexandritelaser, and a Ti:sapphire laser.

Solid-state lasers to be used include, for example, lasers using YAG,YVO₄, YLF, and YAlO₃ crystals that are doped with one of Cr, Nd, Er, Ho,Ce, Co, Ti, or Tm. The fundamental of the laser to be used depends onthe material to be doped, and a laser beam having a fundamental of about1 μm can be obtained. The harmonics corresponding to the fundamental canbe obtained by use of a nonlinear optical element.

To obtain large-diameter crystal in crystallization of the semiconductorfilm, it is preferable that a solid-state laser continually oscillatablebe used to employ a second harmonic, a third harmonic, and a fourthharmonic of a fundamental. Typically, a second harmonic (532 nm) and athird harmonic (355 nm) of Nd:YVO₄ laser light (fundamental: 1064 nm) isemployed.

Laser light emitted from an YVO₄ laser for generating continuousoscillations with a 10 W output is converted by a nonlinear opticaldevice into harmonics. Another usable method is also available in whichan YVO₄ crystal and a nonlinear optical device is included in aresonator to emit harmonics. Preferably, the optical system is used toperform rectification into rectangular or ellipsoidal laser light on anirradiation surface, and the laser light is thereby radiated to aprocessing target. In this case, an energy density of about 0.1 to 100MW/cm³ (preferably, 0.1 to 10 MW/cm²) is necessary. The semiconductorfilm is relatively moved with respect to the laser light at a speed ofabout 0.5 to 2000 cm/s, and is thereby irradiated.

As shown in FIG. 1B, the semiconductor film 103 thus crystallized ispatterned using photolithography, and an island-like crystallinesemiconductor film 104 is thereby formed. In the patterning, a firstphotomask is used.

Subsequently, as shown in FIG. 1C, a second insulation film 105 isformed to a thickness of from 20 nm to 130 nm on one of the substrate101, the first insulation film 102, and the crystalline semiconductorfilm 104. The second insulation film 105 may be any one of a siliconoxynitride film, a silicon oxide film, a nitrogen-containing siliconoxide film, and a silicon nitride film that are deposited using a CVDmethod in which SiH₄ and N₂O are used as source materials.Alternatively, the second insulation film 105 may be formed by combiningand overlapping two or more of the aforementioned films. Then, as shownin FIG. 1D, the second insulation film 105 is patterned usingphotolithography, a portion of the surface of the crystallinesemiconductor film 104 is exposed, and an island-like second insulationfilm 106 to be used as a gate insulation film is thereby formed. In thepatterning, a second photomask is used. Before patterning the secondinsulation film 105, a p-type impurity such as boron may be introducedto the entirety of the crystalline semiconductor film 104. This is awell-known technique generally called “channel doping”, and the channeldoping is performed at a later stage to introduce the p-type impurity toa portion that is to be used as a channel region.

Next, native oxides are removed with dilute hydrofluoric acid watersolution from the surface of the island-like crystalline semiconductorfilm 104 whose surface has been exposed when forming the secondinsulation film 106. Then, as shown in FIG. 1E, the aforementionedsurface is oxidized, and an oxide film 107 is formed. The oxide film 107is formed by applying an oxidizing water solution by use of a spincoating technique on the surface desired to be oxidized. Morespecifically, the substrate 101 on which at least the crystallinesemiconductor film 104 and the second insulation film 106 are formed isrotated. At the same time, ozone (O₃) water solution (which hereinbelowwill be referred to as “ozone water” in the present specification) isapplied to continually flow to the surface of the crystallinesemiconductor film 104 at a room temperature for a time period of from30 seconds to 120 seconds. Ozone is a gas and water-soluble at a normaltemperature and a normal pressure, and exhibits great oxidation effects.The water used as a solvent for the ozone water is deionized watertreated by removing fine foreign matters and impurities, and the ozonewater having a density of from 8 mg/l to 15 mg/l is used. Thereafter,the surface is washed with the deionized water, and the ozone water isthereby removed from the surface. Then, while nitrogen is sprayed, thesubstrate 101 is rotated, and the surface is dried.

The oxide film 107 thus formed is very thin. Therefore, although theprecise film thickness cannot easily be measured, the film 107 is formedwithin a range of from 0.7 nm to 2.0 nm. Even when the time (processingtime) in which the ozone water flows is varied, no significant changesoccur in the thickness of the oxide film that is to be formed; and in atime of from 30 seconds to 120 seconds, the thickness of the oxide filmfalls in a range of from 0.7 nm to 2.0 nm.

To analyze the composition of the oxide film by use of the ozone water,a spectrum of Si2p was measured for an oxide film formed applying ozonewater having a density of 14 mg/l to flow to silicon-wafer surfaces((100) surfaces) at a room temperature for a time period of 60 seconds.The analysis was performed using an analyzer called an “ESCA” (electronspectroscopy for chemical analysis) or an “XPS” (x-ray photoelectronspectroscopy) that is capable of identifying a chemical bond conditionof elements of a specimen surface. The result revealed two peaks ofbinding energy in a range of from 96 to 106 eV. The one is a Si⁴⁺ peak,and the other is a Si peak. Since the Si peak has an oxide film which issmall in film thickness, it is detected from the silicon wafer. Sincethe Si⁴⁺ peak includes small peaks of Si¹⁺, Si²⁺, and Si³⁺, waveformseparation was performed according to Gaussian functions and Lorentzfunctions. Then, according to the peak forms, oxidized condition ofsilicon was analyzed. As a result, with respect to 100% representing thesum of Si¹⁺, Si²⁺, Si³⁺, and Si⁴⁺, the ratios were 8.8% for Si¹⁺, 8.8%for Si²⁺, 6.4% for Si³⁺, and 76.0% for Si^(4÷). Si¹⁺, Si²⁺, and Si³⁺ arereferred to as “suboxides”. The suboxide represents a state where thesilicon did not sufficiently react with oxygen and partly remainedbonded with silicon. Suppose the ratio of Si⁴⁺ is 100%, and the ratiosof the suboxides are each 0%. In this case, it can be determined thatthe oxide film has been sufficiently oxidized and has been formed ofstable SiO₂. The oxide film formed on the surface of the silicon waferby use of the ozone water can be expressed as a silicon oxide filmformed of SiO_(x) (0<X<2) and SiO₂. The thickness of the oxide film wasmeasured by an analyzer called a “spectro-ellipsometry”, and found to be0.81 nm.

As a comparison example, the spectrum of Si2p was measured using theESCA for an oxide film deposited on a silicon wafer by use of a CVDmethod in which Si(OC₂H₅) called “TEOS” and O₂ are used as sourcematerials. Then, analysis was performed as had been performed for theoxide film formed using the ozone water. As a result, with respect to100% representing the sum of Si¹⁺, Si²⁺, Si³⁺, and Si⁴′, the ratios were1.8% for Si¹⁺, 0.9% for Si²⁺, 4.6% for Si³⁺, and 92.7% for Si⁴⁺. Thus,the oxide film deposited using the CVD method was found to exhibit ahigher ratio of SiO₂ than the oxide film formed using the ozone water.

Subsequently, as shown in FIG. 2A, a conductive film 108 is formedoverall on the substrate 101 (or on the first insulation film 102), theoxide film 107, and the island-like second insulation film 106 to athickness of from 200 nm to 500 nm. The conductive film 108 is formed bydepositing a crystalline silicon film containing n-type impurity by useof a CVD method in which the deposition temperature is set to 500° C. orhigher. The crystalline silicon film thus formed is doped with an n-typeimpurity of 1×10⁹ cm⁻³ to 5×10²¹ cm⁻³. For example, phosphorous is usedas the n-type impurity. The conductive film 108 may be multilayered.Specifically, a film made of a heat-resistant material, such astitanium, molybdenum, tungsten, molybdenum silicide, or tungstensilicide, may further be formed on the crystalline silicon filmcontaining the n-type impurity to impart resistance to the conductivefilm 108. Further forming a film formed of titanium nitride, molybdenumnitride, or tungsten nitride between the n-type impurity-containingcrystalline silicon film and the titanium, molybdenum, or tungsten filmenables counter-dispersion to be prevented from occurring between thecrystalline silicon film containing the n-type impurity and the film oftitanium, molybdenum, or tungsten.

Next, as shown in FIG. 2B, a gate electrode 109, a source electrode 110,and a drain electrode 111 are simultaneously formed by patterning theconductive film 108 by use of photolithography. In this case, the oxidefilm 107 operates as an etch stop, thereby causing the crystallinesemiconductor film 104 to remain unetched. The above-describedpatterning is performed using a third photomask.

Subsequently, an n-type impurity such as phosphorous is introduced tothe crystalline semiconductor film 104. The impurity introduction may beperformed by an ion implantation method, which involves mass separation,and an ion doping method, which does not involve mass separation.However, the ion doping method also introduces hydrogen in addition tothe n-type impurity. The introduction is performed such that, in thecrystalline semiconductor film 104, the n-type impurity is introduced tofirst regions covered by only the oxide film 107 and to second regionscovered by only the second insulation film 106, whereas the n-typeimpurity is not introduced to a lower region of the gate electrode 109.As a result, the density of the n-type impurity in the second regions islower than that in the first regions; hence, the second regions referlow-density impurity regions 112 (LDD regions). The first regions areincluded to portions of a source electrode 113 and a drain region 114. Aregion that is located below the gate electrode 109 and that issandwiched by the low-density impurity regions 112 (LDD regions) is usedas a channel region 115. The low-density impurity regions 112 (LDDregions), the source electrode 113, and the drain region 114 can beformed with one-time introduction of the n-type impurity. However, acase can be considered to occur in which the density of the n-typeimpurity to be introduced to the first regions becomes too low to formthe source region 113 and the drain region 114. In this case, the n-typeimpurity needs to separately be introduced two times. In the firstintroduction, the low-density impurity regions 112 (LDD regions) areformed at a high speed and with a low dose so that the n-type impurityis introduced to reach a lower portion of the second insulation film106. In the second introduction, the source electrode 113 and the drainregion 114 are formed with a high dose at a speed lower than that in thefirst introduction. The first and second introductions may be performedin the reverse order.

After the n-type impurity has been introduced as described above, theoxide film 107 still exists between the portion where the sourceelectrode 110 and the drain electrode 111 are formed and the crystallinesemiconductor film 104. As described above, the thickness of the oxidefilm 107 is as small as 0.7 nm to 2.0 nm. However, since high contactresistance occurs between individual portions where the source electrode110 and drain electrode 111 are formed and the crystalline semiconductorfilm 104 is not preferable, the oxide film 107 should not remain. Theoxide film 107 becomes unnecessary upon completion of formation of thegate electrode 109, the source electrode 110, and the drain electrode111. Therefore, even in a case where oxygen is desorbed from the oxidefilm 107, and the oxide film 107 is thereby changed to a film in which anumber of lattice defects have been developed and which no longer hasthe feature of a film, the case is preferable, and no care needs to betaken.

In view of the situation described above, the contact resistance betweenthe source electrode 110 and drain electrode 111 and the crystallinesemiconductor film 104 is reduced to improve the electric conductivity.To achieve the improvement, at least the crystalline semiconductor film104, the oxide film 107, the source electrode 110, and the drainelectrode 111 are heated at a temperature of from 800° C. to 1050° C. ina nitrogen ambient. The heat-treatment ambient is not limited to thenitrogen ambient, and any other inert gas ambients may be used. Theheating time is set to a range of from 30 minutes to 4 hours. When theheating temperature is set to 800° C., the heating time is preferably ina range of from 2 to 4 hours. When the heating temperature is set to950° C., the heating time may be about 30 minutes. The heatingtemperature should not unnecessarily be increased to improve thethroughput. The upper limit of the heating temperature is determineddepending on the type of the substrate 101, the material for forming theconductive film 108, and the heating means. In a configuration includinga stainless steel used for the substrate 101, care needs to be given toa case where antibrittleness and anticorrosion properties of thestainless steel can deteriorate depending on the heating temperature andthe heating time.

When heating has been performed at the aforementioned temperature range,i.e., a temperature of from 800 to 1050° C., the oxide film 107 changesin characteristics so that it no longer functions as an etch stop. Inaddition, damage caused in the crystalline semiconductor film 104 duringthe introduction of the n-type impurity is rectified. Further,crystallinity can be increased for amorphous portions and for regionsinsufficiently crystallized during the crystallization of thesemiconductor film 103, thereby, phosphorous contained in the sourceelectrode 110 and the drain electrode 111 is dispersed into thecrystalline semiconductor film 104. The dispersion works to formphosphorous-introduced impurity regions also in regions below the sourceelectrode 110 and the drain electrode 111 of the crystallinesemiconductor film 104. Consequently, the phosphorous-introducedimpurity regions and the first regions are combined, and the sourceelectrode 113 and the drain region 114 are thereby formed.

The present inventors consider reasons for the change in thecharacteristics of the oxide film 107, as described hereunder. Sinceheating performed at a temperature of from 800° C. to 1050° C. disablesthe oxide film 107 to function as an etch stop, oxygen is desorbed fromthe oxide film 107, SiO_(x) (0<X≦2) composing the oxide film 107 isreduced in the value of “X”, and even the case of “X=0” is thereforeincorporated thereinto. For this reason, the n-type impurity is prone todispersing, thereby improving the electrical conductivity between thesource electrode 110 and drain electrode 111 and the crystallinesemiconductor film 104.

Experiments were performed to clarify that the contact resistance variesaccording to the heat treatment. First, an example was prepared formeasuring the contact resistance, of which a cross section is shown inFIG. 10A. Referring to FIG. 10A, numeral 1001 denotes a quartzsubstrate, numeral 1002 denotes an island-like crystalline silicon filmcontaining phosphorous, numeral 1003 denotes an oxide film, and numeral1004 denotes an electrode. The oxide film 1003 was formed by oxidizingthe surface of the crystalline silicon film 1002 in a process usingozone water. The electrode 1004 is formed by sequentially laminating aphosphorous-containing crystalline silicon film 1005, a tungsten nitridefilm 1006, and a tungsten film 1007. The actual resistance-measurementexample was formed to include continually formed 1,000 portions in eachof which the crystalline silicon film 1002 is covered with the electrode1004 (portion where the crystalline silicon film 1002 and the electrode1004 are formed adjacent to each other via the oxide film 1003). FIG.10A shows only a portion of the cross section of the example.

FIG. 10B shows plotted results of contact-resistance measurementsperformed for the example prepared as described above for eight pointsunder two different conditions respectively, namely, condition 1 andcondition 2. The condition 1 represents a case where heat treatment wasperformed at a temperature of 950° C. for a time period of 30 minutes,and the condition 2 represents a case where the heat treatment was notperformed. The contact resistances are in a range of from 1×10⁵Ω to1×10⁶Ω under the condition 1, the contact resistances are in a range offrom 1×10⁸Ω to 1×10¹³Ω under the condition 2. According to the results,the contact resistances and variations in the eight-point contactresistances under the condition 1, in which the heat treatment wasperformed, are less than those under the condition 2, in which the heattreatment was not performed. Thus, the results show effects of the heattreatment. As described above, since the actual resistance-measurementexample was formed to include continually formed 1,000 portions in eachof which the crystalline silicon film 1002 is covered with the electrode1004, the results can be considered to represent the resistances ofseries-connected 1,000 stages. Therefore, it should be noticed that thecontact resistance of one portion where the crystalline silicon film1002 is covered with the electrode 1004 corresponds to 1/1000 of thevalue shown in FIG. 10B. Accordingly, the contact resistance of oneportion where the crystalline silicon film 1002 is covered with theelectrode 1004 is in a range of from 1×10²Ω to 1×10³Ω under thecondition 1, and is in a range of from 1×10⁵Ω to 1×10¹⁰Ω under thecondition 2.

Next, as shown in FIG. 2C, a third insulation film 116 is formed to athickness of from 100 nm to 1000 nm. The third insulation film 116 maybe any one of a silicon oxynitride film, a silicon nitride oxide film,silicon oxide film, a nitrogen-contained silicon oxide film, and siliconnitride film. The aforementioned silicon oxynitride film is depositedusing a CVD method in which SiH₄ and N₂O are used as source materials;and the aforementioned silicon nitride oxide film is deposited using aCVD method in which SiH₄, N₂O, and NH₃ are used as source materials.Alternatively, the third insulation film 116 may be formed by combiningand overlaying two or more of the aforementioned films. Thereafter, thecrystalline semiconductor film 104, the gate electrode 109, the sourceelectrode 110, and the drain electrode 111 are heated at a temperatureof from 800° C. to 1050° C. in a nitrogen ambient for a time period offrom 30 minutes to 2 hours to cause the n-type impurity contained in thefilms to be active. In this case, the nitrogen ambient may containhydrogen and after the heat treatment in the nitrogen ambient, the filmsmay be heated in an ambient containing nitrogen and hydrogen for aboutone hour. When the n-type impurity has sufficiently been activated bythe heat treatment performed at a temperature of from 800° C. to 1050°C. to change the characteristics of the oxide film 107, the heattreatment in the nitrogen ambient for activating the n-type impurity maybe omitted. Further, instead of performing the heat treatment in anitrogen ambient at a temperature of from 800° C. to 1050° C. for a timeperiod of from 30 minutes to 4 hours before the third insulation film116 is formed, a heat treatment may be performed in a nitrogen ambientat a temperature of from 800° C. to 1050° C. for a time period of from30 minutes to 4 hours after the third insulation film 116 has beenformed. In this case, the third insulation film 116 operates as apassivation film during the heat treatment.

Subsequently, as shown in FIG. 2D, a fourth insulation film 117 isformed on the third insulation film 116 to obtain a planar surface. Thefourth insulation film 117 may be formed using an organic resin, such asa polyimide resin, an acrylic resin, or benzocyclobutene (BCB).Alternatively, the insulation film 117 may be formed using a siliconoxide film formed by using a coating technique called “SOG technique”(spin-on-glass technique). Still alternatively, the fourth insulationfilm 117 may be formed by polishing a surface of an inorganic insulationfilm such as a silicon oxide film by use of a well-knownchemical-mechanical polishing (CMP) technique. Then, the thirdinsulation film 116 and the fourth insulation film 117 are patternedusing photolithography, and an opening 118 is formed to reach the drainelectrode 111 (or the source electrode 110). The patterning uses afourth photomask.

Next, as shown in FIG. 2E, after a transparent conductive film is formedoverall on the fourth insulation film 117 to a thickness of from 50 nmto 150 nm, a pixel electrode 119 is formed by performing patterningaccording to well-known photolithography. The transparent conductivefilm may be formed of any one of tin oxide, a compound called “indiumtin oxide (ITO)” made of indium oxide and tin oxide, and a compound ofindium oxide and zinc oxide. The aforementioned patterning uses a fifthphotomask.

As described above, in the present embodiment mode, three patterningsteps are performed in the processing to complete formation of thesource electrode 110 and the drain electrode 111, and three photomasksare used during the processing. However, in the processing described inSection “Description of the Related Art” of this document, fourpatterning steps are performed in the processing to complete theformation of the source electrode and the drain electrode, and fourphotomasks are used during the processing. Thus, compared to the relatedart, in the present embodiment mode, the patterning steps can be reducedby one step, and the photomasks can be reduced by one piece. Inaddition, the present embodiment mode has advantages described hereundersince the gate electrode 109, source electrode 110, and the drainelectrode 111 are simultaneously formed using only one photomask. Thepresent embodiment mode enables the interface pitch between the gateelectrode 109 and the source electrode 110 and the interface pitchbetween the gate electrode 109 and the drain electrode 111 to easily bemodified. The minimum value of each of the interface pitches isdetermined by design rules, and the interface pitch may be reduced asmuch as the design rules permit, without considering margins. Thus, thetransistor size can be reduced to enhance the integration density of thetransistor. In addition, the present invention enables the area of aportion where the source electrode 113 is covered with the sourceelectrode 110 and the area of a portion where the drain region 114 iscovered with the drain electrode 111 to easily be modified so thatoptimal electrical characteristics can be obtained.

(Second Embodiment Mode)

The first embodiment mode uses the crystalline silicon film containingthe n-type impurity for the conductive film 108 that is used to form thegate electrode 109, the source electrode 110, and the drain electrode111. However, in the present embodiment mode, a crystalline silicon filmcontaining n-type impurity needs not be used for a conductive film. Thepresent embodiment mode is dissimilar to the first embodiment mode inthat the second insulation film 106 is used as a mask to introduceeither n-type impurity or p-type impurity to the crystallinesemiconductor film 104 before the conductive film 108 is formed.Processes corresponding those shown to FIGS. 1A to 1D are common tothose in the first embodiment mode of the present invention. Thus, onlyprocesses subsequent to the process corresponding to that shown FIG. 1Dwill be described hereunder with reference to FIGS. 3A to 3E.

After completion of the forming processes to the stage shown in FIG. 1D,the n-type impurity such as phosphorous is introduced to the crystallinesemiconductor film 104 by use of the island-like second insulation film106 as a mask. The n-type impurity is not introduced to a portioncovered with the second insulation film 106, and the impurity isintroduced to a portion not covered by the second insulation film 106.Then, a source region 313 and a drain region 314 are formed. Theintroduction of the n-type impurity may be performed by any one of anion implantation method that involves mass separation and an ion dopingmethod that does not involve mass separation. In the present embodimentmode, instead of the n-type impurity, a p-type impurity such as boronmay be used. Thereafter, as shown in FIG. 3A, an oxide film 307 isformed in the same methods as those in the first embodiment mode of thepresent invention.

Subsequently, as shown in FIG. 3A, a conductive film 308 is formedoverall on the substrate 101 or the first insulation film 102, the oxidefilm 307, and the island-like second insulation film 106 to a thicknessof from 200 nm to 500 nm. The conductive film 308 may be formed of anyone of, for example, copper, palladium, chromium, cobalt, titanium,molybdenum, niobium, tantalum, and tungsten. Still alternatively, theconductive film 308 may be formed in combination with, for example,titanium nitride, tantalum nitride, tungsten nitride, cobalt silicide,titanium silicide, molybdenum silicide, niobium silicide, tantalumsilicide, or tungsten silicide. In addition, similarly to the firstembodiment mode, crystalline silicon containing the n-type impurity maybe used as at least a portion of materials composing the conductive film308.

Next, as shown in FIG. 3B, a gate electrode 309, a source electrode 310,and a drain electrode 311 are simultaneously formed by patterning theconductive film 308 by use of photolithography. In this case, the oxidefilm 307 operates as an etch stop, thereby causing the crystallinesemiconductor film 104 to remain unetched.

Subsequently, an n-type impurity such as phosphorous is introduced againto a region covered only by the second insulation film 106 in thecrystalline semiconductor film 104 to thereby form low-density impurityregions 312 (LDD regions). The density of the n-type impurity in thelow-density impurity regions 312 (LDD regions) is lower than that in thesource region 313 and the drain region 314. A region that is below thegate electrode 309 and sandwiched by the low-density impurity regions312 (LDD regions) is not doped with the n-type impurity, and is used asa channel region 315. Instead of the n-type impurity, p-type impuritymay be used. Then, at least the crystalline semiconductor film 104, theoxide film 307, the source electrode 310, and the drain electrode 311are heated at a temperature of from 800° C. to 1050° C. for a timeperiod of from 30 minutes to 4 hours in a nitrogen ambient. The heatingambient is not limited to the nitrogen ambient, but any other inert gasambients may be used. The above-described heating works to reduce thecontact resistance between the source electrode 310 and the sourceregion 313 as well as the contact resistance between the drain electrode311 and the drain region 314.

Next, as shown in FIG. 3C, a third insulation film 316 is formed to athickness of from 100 nm to 1000 nm. The third insulation film 316 maybe any one of a silicon oxynitride film, a silicon nitride oxide film,silicon oxide film, and silicon nitride film. The aforementioned siliconoxynitride film is deposited using a CVD method in which SiH₄ and N₂Oare used as source materials; and the aforementioned silicon nitrideoxide film is deposited using a CVD method in which SiH₄, N₂O, and NH₃are used as source materials. Alternatively, the third insulation film316 may be formed by combining and overlaying two or more of theaforementioned films. Further, as described above, the heat treatment inthe nitrogen ambient at a temperature of from 800° C. to 1050° C. for atime period of from 30 minutes to 4 hours before the third insulationfilm 316 is performed. Instead of the heat treatment, however, a heattreatment may instead be performed in a nitrogen ambient at atemperature of from 800° C. to 1050° C. for a time period of from 30minutes to 4 hours after the third insulation film 316 has been formed.

Subsequently, as shown in FIG. 3D, a fourth insulation film 317 having athickness of from 1000 nm to 4000 nm is formed on the third insulationfilm 316 to obtain a planar surface. The fourth insulation film 317 maybe formed using an organic resin, such as a polyimide resin, an acrylicresin, or benzocyclobutene (BCB). Alternatively, the film 317 may beformed using a silicon oxide film formed using a coating techniquecalled a “SOG technique”. Then, the third insulation film 316 and thefourth insulation film 317 are patterned using photolithography, and anopening 318 is formed to reach the drain electrode 311 (or the sourceelectrode 310).

Next, as shown in FIG. 3E, after a transparent conductive film is formedoverall on the fourth insulation film 317, a pixel electrode 319 isformed by performing patterning according to well-knownphotolithography. The transparent conductive film may be formed of anyone of tin oxide, a compound called “indium tin oxide (ITO)” made ofindium oxide and tin oxide, and a compound of indium oxide and zincoxide.

As described above, similarly to the first embodiment mode of thepresent invention, in the present embodiment mode, three patterningsteps are performed in the processing to complete formation of thesource electrode 310 and the drain electrode 311, and three photomasksare used during the processing. Thus, according to the presentembodiment mode, compared to the conventional art, the patterning stepscan be reduced by one step and the photomasks can be reduced by onepiece. In addition, the present embodiment mode has advantages describedhereunder since the gate electrode 309, source electrode 310, and thedrain electrode 311 are simultaneously formed using only one photomask.The present embodiment mode enables the interface pitch between the gateelectrode 309 and the source electrode 310 and the interface pitchbetween the gate electrode 309 and the drain electrode 311 to easily bemodified. Thus, the transistor size can be reduced to enhance theintegration density of the transistor. In addition, the presentinvention enables the area where the source electrode 313 is coveredwith the source electrode 310 and the area where the drain region 314 iscovered with the drain electrode 311 to easily be modified, so thatoptimal electrical characteristics can be obtained.

(Third Embodiment Mode)

As described above, in the first embodiment mode of the presentinvention, the ozone water is used to form the oxide film 107. However,in a third embodiment mode, water solution of hydrogen peroxide (H₂O₂)(which hereinbelow will be referred to as “hydrogen peroxide water” inthe present specification) is used for the film formation. Hereinbelow,the present embodiment mode will be described only for mattersdissimilar to the first embodiment mode.

The substrate 101 on which at least the crystalline semiconductor film104 and the second insulation film 106 are formed is rotated. During therotation, hydrogen peroxide water of a room temperature or a temperatureof 80° C. is applied so as to continually flow to the surface of thecrystalline semiconductor film 104 for a time period of from 30 secondsto 600 seconds. For the hydrogen peroxide water, hydrogen peroxide watersolution having a density of from 30 wt % to 35 wt % (31 wt % forexample) is used. Hydrogen peroxide is liquid and water-soluble at anormal temperature and a normal pressure, and exhibits oxidationeffects. As in the case of the ozone water, the deionized water is usedas a solvent.

As in the first embodiment mode, also the oxide film formed in thepresent embodiment mode is very thin. Therefore, although the precisefilm thickness cannot easily be measured, the film is formed within arange of from 0.7 nm to 1.5 rim when processed in the room temperatureor within a range of from 1.0 nm to 2.0 nm when processed at atemperature of 80° C. Even when the time (processing time) in which thehydrogen peroxide water flows changes, no significant variations occurin the thickness of the oxide film that is to be formed.

Subsequent processes are similar to those in the first embodiment modeof present invention. However, as described in the second embodimentmode, the conductive film 108 is formed of any one of, for example,copper, palladium, chromium, cobalt, titanium, molybdenum, niobium,tantalum, and tungsten. Further, the conductive film 108 is combinedwith, for example, titanium nitride, tantalum nitride, tungsten nitride,cobalt silicide, titanium silicide, molybdenum silicide, niobiumsilicide, tantalum silicide, or tungsten silicide. In this case, thecrystalline silicon film containing the n-type impurity need not beused, and processes may be performed according to the processes in thesecond embodiment mode.

(Fourth Embodiment Mode)

As described above, in the first embodiment mode of the presentinvention, the first insulation film 102 is formed on the substrate 101.However, in a fourth embodiment mode, a light-shielding film is providedbetween the substrate 101 and the first insulation film 102.Hereinbelow, referring to FIGS. 4A to 4C, the present embodiment modewill be described only for matters dissimilar to the first embodimentmode.

As shown in FIG. 4A, a light shield film 400 is formed to a thickness offrom 100 nm to 300 nm on the substrate 101. The light-shielding film 400is formed to prevent the crystalline semiconductor film 104, which willbe formed later, from being irradiated. The light-shielding film 400 ispatterned and formed in an island shape so as to overlap at least thechannel region of the crystalline semiconductor film 104. Thelight-shielding film 400 may be formed using, for example, one ofchromium, tungsten, molybdenum, niobium, tantalum, titanium, titaniumsilicide, molybdenum silicide, niobium silicide, tantalum silicide, andtungsten silicide films. Alternatively, the light-shielding film 400 maybe formed in a so-called polyside structure, which is formed bylaminating a metal silicide film such as a tungsten silicide film on acrystalline silicon film containing n-type impurity. When thelight-shielding film 400 is formed of a conductive film, it can be usedto function as a gate electrode.

Next, as in the first embodiment mode, as shown in FIG. 4B, the firstinsulation film 102, the island-like crystalline semiconductor film 104,and the second insulation film 105 are formed. Then, a p-type impurityfor channel doping is introduced to the crystalline semiconductor film104. In the process of forming the first insulation film 102, the firstinsulation film 102 may be formed to a thickness greater than that ofthe light-shielding film 400, and the surface of the first insulationfilm 102 may be polished to be levelled by using the well-knownchemical-mechanical polishing (CMP) technique.

Subsequently, as shown in FIG. 4C, the second insulation film 105 andthe first insulation film 102 are patterned using photolithography, andan opening 401 is formed. The opening 401 is formed to electricallyconnect a gate electrode 109 which will be formed later and thelight-shielding film 400; the opening is not provided to the crystallinesemiconductor film 104. When the light-shielding film 400 is notconductive, the opening 401 is not provided thereto. Next, the secondinsulation film 105 is patterned using photolithography, and anisland-like second insulation film 106 is thereby formed.

Subsequent processes are similar to those in the first embodiment modeof present invention, that is, the processes may be performed as shownin FIGS. 1E and 2A to 2E. However, to form the oxide film 107, thehydrogen peroxide water as described in the third embodiment mode may beused. In addition, the conductive film 108 needs to be formed tocompletely fill up the opening 401. As described in the secondembodiment mode, the conductive film 108 is formed of any one of, forexample, copper, palladium, chromium, cobalt, titanium, molybdenum,niobium, tantalum, and tungsten. Further, the conductive film 108 iscombined with, for example, titanium nitride, tantalum nitride, tungstennitride, cobalt silicide, titanium silicide, molybdenum silicide,niobium silicide, tantalum silicide, or tungsten silicide. In this case,the crystalline silicon film containing the n-type impurity need not beused, and processes may be performed according to the processes in thesecond embodiment mode.

Hereinbelow, further practical embodiments relative to the embodimentmodes of the present invention will be described.

(First Embodiment)

In a first embodiment, a manufacturing method for an active matrixliquid crystal display device (AMLCD) employing the first and fourthembodiment modes of the present invention will be described withreference to FIGS. 5A to 5E, 6A to 6E, and 7A to 7C. First, as shown inFIG. 5A, a crystalline silicon film and a tungsten silicide film areformed on a quartz substrate 501 by well-known techniques. In thepresent embodiment, the crystalline silicon film is formed according toan LPCVD method in which SiH₄ and PH₃ are used as source materials, andthe deposition temperature is set to 600° C. Then, a target formed oftungsten and silicon is sputtered with argon ions, and the tungstensilicide film is thereby formed on the crystalline silicon film. Thetungsten silicide film may be formed by other techniques, such as a CVDmethod using WF₆ and SiH₂Cl₂ as source materials. Then, the crystallinesilicon film and the tungsten silicide film are patterned usingphotolithography, and a first light-shielding film 502 is therebyformed.

Subsequently, as shown in FIG. 5B, a silicon oxynitride film 503 isformed on the first light-shielding film 502 according to a plasma CVDmethod using SiH₄ and N₂O as source materials. Further, a silicon oxidefilm 504 is formed on the first light-shielding film 502 by using anLPCVD method in which the deposition temperature is set to 800° C., anda reaction chamber is maintained in decompressed state. The siliconoxynitride film 503 is formed to prevent an LPCVD system, which is to beused to subsequently form the silicon oxide film 504, from beingcontaminated by materials forming the first light-shielding film 502.Therefore, if no probability exists that the LPCVD system iscontaminated, the silicon oxynitride film 503 need not be formed. Thesilicon oxynitride film 503 and the silicon oxide film 504 correspond tothe first insulation film 102 in the first and fourth embodiment modes,respectively. Subsequently, a silicon film 505 is formed by an LPCVDmethod on the silicon oxide film 504.

Next, the quartz substrate 501 is rotated, while being coated withsolution containing nickel as an element accelerates crystallization ofsilicon films, specifically, nickel acetate solution in the presentembodiment by using a spin coating technique. Then, while the quartzsubstrate 501 is rotated, an excessive amount of the nickel acetatesolution is removed to dry the substrate. Subsequently, heat treatmentis conducted using an electric furnace at a temperature of 450° C. forone hour to cause hydrogen contained in the silicon film 505 to bereleased. In addition, heat treatment is conducted using an electricfurnace at a temperature of 600° C. for 12 hours to cause the siliconfilm 505 to be crystallized.

As an alternative method of crystallizing the silicon film 505, themethod described hereunder may be used. Solid-state laser light formedin a rectangular form (second harmonic (532 nm) of an Nd:YVO₄ laser) isirradiated to the silicon film 505. The light having a 532 nm wavelengthhas a characteristic in that it is not substantially absorbed into thequartz substrate 501, while it is absorbed into the silicon film 505.Therefore, the time required for crystallization of a silicon film canbe more reduced by using laser irradiation than by heating the film inan electric furnace. In this case, the step of applying thenickel-contained solution as well as a gettering step described belowcan be omitted from the manufacturing procedure.

Subsequently, nickel contained in the crystallized silicon film 505needs to be gettered to thereby be removed. First, a silicon oxide filmis formed on the crystallized silicon film 505 by using an LPCVD methodin which the deposition temperature is set to 400° C. Then, the filmthus formed is patterned using photolithography, and a mask 506 as shownin FIG. 5C is thereby formed. The mask 506 is formed to introducephosphorous to only a portion of the crystallized silicon film 505.

Next, phosphorous is introduced from the mask 506 to the crystallizedsilicon film 505 according to an ion-doping method under a condition of10 kV and 2×10¹⁵ cm⁻². As a result, the phosphorous is introduced to aregion 507. Thereafter, upon heating of the crystallized silicon film505 at a temperature of 700° C. for 12 hours in a nitrogen ambient,nickel in the crystallized silicon film 505 transfers to the region 507.

Subsequently, as shown in FIG. 5D, the mask 506 is etched and removed,and in addition, the crystallized silicon film 505 is patterned usingphotolithography. Thereby, an island-like crystalline silicon film 508is formed. In this state, the region 507 is totally removed. Inaddition, the crystalline silicon film 508 is formed to completelyoverlap the first light-shielding film 502.

Next, as shown in FIG. 5E, a silicon oxynitride film 509 is formed by aplasma CVD method in which SiH₄ and N₂O are used as source materials.Then, channel doping is performed by introducing boron under a conditionof 60 kV and 3.6×10¹³ cm⁻² to the entirety of the crystalline siliconfilm 508.

Subsequently, as shown in FIG. 6A, pattering is performed usingphotolithography to form an opening 510 through the silicon oxynitridefilm 503, the silicon oxide film 504, and the silicon oxynitride film509 so as to reach the light-shielding film 502. The opening 510 is notformed for the crystalline silicon film 508. Then, the siliconoxynitride film 509 is patterned using photolithography, and anisland-like gate insulation film 511 is thereby formed.

Next, as shown in FIG. 6B, an island-like silicon oxide film 512 isformed on the surface of the crystalline silicon film 508. The siliconoxide film 512 is formed by the method described in the first embodimentmode of the present invention. Specifically, native oxides are removedby dilute hydrofluoric acid water solution from the surface ofcrystalline silicon film 508 whose surface has been exposed when formingthe gate insulation film 511. Then, a spin coating technique isperformed. In the coating process, the quartz substrate 501 on which thefirst light-shielding film 502, the silicon oxynitride film 503, thesilicon oxide film 504, the crystalline silicon film 508, and the gateinsulation film 511 are formed is rotated. At the same time, ozone waterhaving a density of 14 mg/l is applied to continually flow to thesurface of the crystalline silicon film 508 at a room temperature for atime period of 60 seconds. Thereafter, the surface is washed with thedeionized water, and the ozone water is thereby removed from thesurface. Then, while nitrogen is sprayed, the substrate 501 is rotated,and the surface is dried. As a result, the formed silicon oxide film 512contains Si¹⁺, Si²⁺, Si³⁺, and Si⁴⁺. In other words, the film 512contains SiO_(x) (0<X<2) and SiO₂.

Subsequently, as shown in FIG. 6C, a phosphorous-containing crystallinesilicon film 513 is formed on the silicon oxide film 504, the siliconoxide film 512, and the gate insulation film 511 according to an LPCVDmethod in which SiH₄ and PH₃ are used as source materials, and thedeposition temperature is set to 600° C.

Next, as shown in FIG. 6D, the phosphorous-containing crystallinesilicon film 513 is patterned using photolithography, thereby, a gateelectrode 514, a source electrode 515, and a drain electrode 516 aresimultaneously formed. As an etching process in the patterning, wetetching using alkaline solution is employed. In this case, the oxidefilm 512 operates as an etch stop, thereby causing the crystallinesilicon film 508 to remain unetched.

Subsequently, phosphorous is introduced to the crystalline silicon film508 by using an ion doping method. First, phosphorous is introduced to aregion covered by only the gate insulation film 511 in the crystallinesilicon film 508 under a condition of 60 kV and 5×10¹³ cm⁻² in order toform low-density impurity regions 517 (LDD regions). Then, thephosphorous is introduced to a region covered by only the silicon oxidefilm 512 in the crystalline silicon film 508 under a condition of 50 kVand 2×10¹⁵ cm⁻² in order to form a source region 519 and a drain region520. The phosphorous is not introduced to a region that is located belowthe gate electrode 514 and that is sandwiched by the low-densityimpurity regions 517 (LDD regions), and the region is used as a channelregion 518. After the gate insulation film 511 has been formed andbefore the silicon oxide film 512 is formed, the phosphorous may beintroduced to the crystalline silicon film 508 to form the source region519 and the drain region 520. This obviates the necessity of thephosphorous introduction step that is performed after the formation ofthe low-density impurity regions 517 (LDD regions) in order to form thesource region 519 and the drain region 520.

After the phosphorous has been introduced in the above-described manner,the silicon oxide film 512 still exists between the portion where thesource region 519 and the source electrode 515 are formed and theportion where the drain region 520 and the drain electrode 516 areformed. In addition, the phosphorous having a density sufficient enoughto form a source region and a drain region is not introduced to theportion covered by the drain electrode 516 in the source region 519 andto the portion covered by the drain electrode 516 in the drain region520. Therefore, using an electric furnace, the quartz substrate 501 onwhich at least the crystalline silicon film 508, the silicon oxide film512, the source electrode 515, and the drain electrode 516 are formed isheated at a temperature of 950° C. for a time period of 30 minutes in anitrogen ambient, thereby, the phosphorous is dispersed from the sourceelectrode 515 and the drain electrode 516 to the source region 519 andthe drain region 520. The heating therefore works to reduce the contactresistance between the source region 519 and the source electrode 515and the contact resistance between the drain region 520 and the drainelectrode 516.

Next, as shown in FIG. 7A, a silicon oxynitride film is formed by aplasma CVD method in which SiH₄ and N₂O are used as source materials,and the formed film is used as an interlayer insulation film 521.Thereafter, heating is performed at a temperature of 950° C. for a timeperiod of 30 minutes in a nitrogen ambient to activate the n-typeimpurity contained in each of the crystalline silicon film 508, the gateelectrode 514, the source electrode 515, and the drain electrode 516.Then, heating is performed at a temperature of 350° C. for one hour in ahydrogen-ambient. As a result, hydrogen terminates dangling bonds (classof defects) in the silicon used to form the crystalline silicon film508, the gate electrode 514, the source electrode 515, and the drainelectrode 516.

Subsequently, as shown in FIG. 7B, an acrylic resin film is formed as aplanarizing film 522 on the interlayer insulation film 521. Instead ofthe planarizing film 522, the film may be, for example, a polyimideresin film, a benzocyclobutene (BCB) film, or a silicon oxide filmformed using a coating technique (SOG technique).

Next, as shown in FIG. 7C, an aluminum-titanium alloy film is formedusing a sputtering process and is then patterned using photolithographyto form a second light-shielding film 523. In the present embodiment, toform a film having light-shielding effects and electroconductivity forthe second light-shielding film 523, the film may be formed of metal,such as chromium, a conductive polymeric material (polymeric materialthat exhibits electroconductivity), or a conductive resin (resin mixedwith a conductive material such as metal and carbon) instead of thealuminum-titanium alloy. To form an insulation film 524 on the secondlight-shielding film 523, a silicon nitride oxide film is formed using aplasma CVD method in which SiH₄, N₂O, and NH₃ are used as sourcematerials. Then, the interlayer insulation film 521, the planarizingfilm 522, and the insulation film 524 are patterned usingphotolithography, and an opening is formed so as to reach the drainelectrode 516 (or the source electrode 515). Next, a transparentconductive film is formed of ITO on the insulation film 524, and theformed film is then patterned. In this manner, a pixel electrode 525 isformed. In the present embodiment, the transparent conductive film maybe formed using a compound of indium oxide and zinc oxide instead ofusing the ITO.

As is apparent from FIG. 7C, a capacitor is formed by the secondlight-shielding film 523, which is the conductive film, the pixelelectrode 525, and the insulation film 524 formed therebetween.

The processes described above partially complete the manufacturingmethod up to the stage where pixel electrodes of the active matrixliquid crystal display device are formed on the substrate on the sidewhere thin-film transistors are formed. Thereafter, the liquid crystaldisplay device may be completed employing well-known techniques.

(Second Embodiment)

A second embodiment is described to disclose another technique ofgettering the nickel contained in the crystallized silicon film 505described in the first embodiment of the present invention. Only mattersdissimilar to those discussed in the first embodiment will be describedhereunder.

This embodiment is similar to the first embodiment of the invention inprocessing up to the state where the nickel acetate solution is appliedto the crystallized silicon film 505 shown in FIG. 5B, and thecrystallized silicon film 505 is heated and crystallized.

After the above state, native oxides are removed with the dilutehydrofluoric acid solution from the surface of the crystallized siliconfilm 505, and an oxide film 806 as shown in FIG. 8A is formed by use ofozone water in the manner similar to that in the first embodiment of theinvention. Then, an amorphous silicon film 807 is formed on a siliconoxide film 806 by use of an LPCVD method. Thereby, argon, which is anoble gas element, is thereby introduced to the amorphous silicon film807. For the introduction, instead of the argon, any one of helium,neon, krypton, and xenon may be used.

Subsequently, heating is conducted at a temperature of 550° C. for fourhours in an electric furnace. Because of the heating, the nickelcontained in the crystallized silicon film 505 passes through thesilicon oxide film 806 and transfers to the amorphous silicon film 807to which the argon has been introduced. Thereby, the nickel is gettered.The heating temperature may be 550° C. or higher, and the upper limit ofthe heating temperature is determined depending on the performance of afurnace and a substrate that are used. In addition, an increase in theheating temperature enables the gettering even in a heating time shorterthan four hours.

Next, the amorphous silicon film 807 is removed in a wet etching processusing alkaline solution. In the wet etching process, since the siliconoxide film 806 operates as an etch stop, the crystallized silicon film505 remains unetched. Consequently, the density of the nickel in thecrystallized silicon film 505 can be reduced to a level of 1×10¹⁷ cm⁻³or lower.

Subsequently, as shown in FIG. 8B, the crystallized silicon film 505 ispatterned using photolithography, and an island-like crystalline siliconfilm 808 is thereby formed. The silicon oxide film 806 remains on onlythe upper surface of the crystalline silicon film 808, whereas it doesnot remain on sidewalls thereof.

Next, as shown in FIG. 8C, an opening 810 and a gate insulation film 811are formed in a manner similar to that in the first embodiment of thepresent invention. When forming the island-like gate insulation film 811by performing patterning, a portion of the silicon oxide film 806 thatis not covered by the gate insulation film 811 is etched. Therefore, theozone water is used again, and a silicon oxide film 812 as shown in FIG.8D is formed in a manner similar to that in the first embodiment of thepresent invention.

Since subsequent processes are similar to those in the first embodimentof present invention, the processes may be performed as shown in FIGS.6C, 6D, and 7A to 7C.

(Third Embodiment)

A second embodiment is described to disclose an active matrix displaydevice that uses LEDs (light emitting devices) and that is manufacturedemploying the first and second embodiments of the present invention.

FIG. 9 is a cross-sectional view of a pixel portion of the displaydevice. Ordinarily, one switching thin-film transistor connected to agate signal line and a source signal line and one current-controllingthin-film transistor (also called a “driving thin-film transistor”)connected to an LED are provided in units of one pixel. However, FIG. 9shows only the current-controlling thin-film transistor. Although thedriving thin-film transistor may be either a p-channel thin-filmtransistor or an n-channel thin-film transistor, the p-channel thin-filmtransistor is used in the present embodiment.

The pixel portion includes a first insulation film 902, an island-likecrystalline silicon film 903, an island-like gate insulation film 904(second insulation film), a gate electrode 905, a source electrode 906,and a drain electrode 907 on a quartz substrate 901. The gate electrode905, the source electrode 906, and the drain electrode 907 are formed ona same conductive material. The island-like crystalline silicon film 903includes a source region, a drain region, and low-density impurityregions (LDD regions) that contain boron as p-type impurity. Inaddition, the crystalline silicon film 903 includes SiO_(x) (0<X<2) (notshown) between the source electrode 906 and the source region andbetween the drain electrode 907 and the drain region. SiO_(x) (0<X<2)may be provided either in the form of a film or not in the form of afilm.

In addition, the pixel portion includes a third insulation film 908 anda planarizing film 909 that are provided in such a manner as to coverthe gate electrode 905, the source electrode 906; and the drainelectrode 907. Further included therein are an anode 910 that is formedof a transparent conductive film (ITO) having a large work function andthat is connected to the drain electrode 907; and a fourth insulationfilm 911 formed on the anode 910. The fourth insulation film 911 has anopening to cause a portion of the surface of the anode 910 to beexposed.

Further, the pixel portion includes an organic compound film 912 that isformed in contact with the anode 910 on the fourth insulation film 911and that includes a luminescent element, and a cathode 913 formed ofeither a metal or an alloy (Mg—Ag alloy) that has a small work function.The anode 910, the organic compound film 912 including the luminescentelement, and the cathode 913 together forms the LED. The active matrixdisplay device using the LEDs according to the present embodiment is ofa downward-radiation type in which light is radiated from the LEDs tothe quartz substrate 901.

(Fourth Embodiment)

In a fourth embodiment, various example products each including adisplay device of the type manufactured according to the presentinvention will be enumerated. The display device is one of an activematrix liquid crystal display device and an active matrix display deviceusing LEDs.

Although not illustrated in the drawings, the display devicemanufactured according to the present invention is used for a displaydevice section of one of various electronic devices, such as a notebookpersonal computer, a cellular phone, a digital camera, a video camera, apersonal digital assistant (PDA), a TV set, a car navigation system, anda head-mounted display device. In addition, the present invention isused for a display device built into either a front-end projector or arear-end projector.

The present invention is based on attention paid to an oxide film thatis formed through a process of a semiconductor surface by use of ozonewater or hydrogen peroxide water. By using the oxide film as an etchstop, the gate electrode, the source electrode, and the drain electrodeof a field-effect transistor can be simultaneously formed using a singlephotomask in a single patterning step. Therefore, the interface pitchbetween the gate electrode and the source electrode and the interfacepitch between the gate electrode and the drain electrode can be reducedas much as possible. Concurrently, the area where the source electrodecovers a source region and the area where the drain electrode covers adrain region can easily be changed. In addition, the present inventionobviates the necessity of performing patterning for providing an openingto an interlayer insulation film to couple the source electrode to thesource region and to couple the drain electrode to the drain region.After the gate electrode, the source electrode, and the drain electrodehave been formed, heating is performed at a high temperature of 800° C.or higher for a predetermined time. As a result, even while theaforementioned oxide film remains, the electrical conductivity betweenthe source electrode and the source region and the electricalconductivity between the drain electrode and the drain region can besufficiently maintained.

According to the present invention, the number of patterning steps andthe number of photomasks can be reduced. Further, the throughput and theyield can be improved. Furthermore, either an active matrix liquidcrystal display device or a LED-using active matrix display deviceaccording to the present invention can be applied to a display devicesection of an electronic device or to one of a variety of products thatincludes a built-in electronic device.

Although the present embodiments have disclosed a thin-film transistor,the present invention is not limited to the thin-film transistor. Thepresent invention can be also apply to the bulk-type IGFET(Insulated-Gate Field Effect Transistor) which is formed on the siliconsubstrate.

What is claimed is:
 1. A manufacturing method for a field-effecttransistor, comprising the steps of: forming a first insulation filmover a crystalline semiconductor film; patterning the first insulationfilm to form a gate insulation film over a portion of the crystallinesemiconductor film; oxidizing a surface of the crystalline semiconductorfilm with an oxidizing water solution to form an oxide film; forming aconductive film over the oxide film and the gate insulation film, theconductive film comprising a semiconductor film containing an impurityhaving one conductivity type; patterning the conductive film to form agate electrode, a source electrode, a drain electrode; and heating thecrystalline semiconductor film, the oxide film, the gate insulationfilm, the gate electrode, the source electrode, and the drain electrodein an inert gas ambient at a temperature of from 800° C. to 1050° C. fora time period of from 30 minutes to 4 hours.
 2. A manufacturing methodfor a field-effect transistor according to claim 1, wherein the impuritycontained in the source electrode and the impurity contained in thedrain electrode are dispersed to the crystalline semiconductor film inheating the crystalline semiconductor film, the oxide film, the gateinsulation film, the gate electrode, the source electrode, and the drainelectrode.
 3. A manufacturing method for a field-effect transistoraccording to claim 1, wherein the oxidizing water solution is one ofozone water solution and hydrogen peroxide water solution.
 4. Amanufacturing method for a field-effect transistor according to claim 1,wherein said one conductivity is an n-type conductivity.
 5. Amanufacturing method for a field-effect transistor according to claim 1,wherein said one conductivity is a p-type conductivity.
 6. Amanufacturing method for a field-effect transistor, comprising the stepsof: forming a semiconductor film over a substrate; crystallizing thesemiconductor film to form a crystalline semiconductor film; patterningthe crystalline semiconductor film to form an island-like crystallinesemiconductor film; forming a first insulation film over the island-likecrystalline semiconductor film; patterning the first insulation film toform a gate insulation film over a portion of the island-likecrystalline semiconductor film; oxidizing a surface of the island-likecrystalline semiconductor film with an oxidizing water solution to forman oxide film; forming a conductive film over the substrate, and overthe oxide film and the gate insulation film, the conductive filmcomprising a semiconductor film containing an impurity having oneconductivity type; patterning the conductive film to form a gateelectrode, a source electrode, a drain electrode; and heating thesubstrate having at least the island-like crystalline semiconductorfilm, the oxide film, the gate insulation film, the gate electrode, thesource electrode, and the drain electrode formed thereon, in an inertgas ambient at a temperature of from 800° C. to 1050° C. for a timeperiod of from 30 minutes to 4 hours.
 7. A manufacturing method for afield-effect transistor according to claim 6, wherein the impuritycontained in the source electrode and the impurity contained in thedrain electrode are dispersed to the island-like crystallinesemiconductor film in heating.
 8. A manufacturing method for afield-effect transistor according to claim 6, wherein the substrate is aquartz substrate.
 9. A manufacturing method for a field-effecttransistor according to claim 6, wherein the oxidizing water solution isone of ozone water solution and hydrogen peroxide water solution.
 10. Amanufacturing method for a field-effect transistor according to claim 6,wherein said one conductivity is an n-type conductivity.
 11. Amanufacturing method for a field-effect transistor according to claim 6,wherein said one conductivity is a p-type conductivity.
 12. Amanufacturing method for a field-effect transistor, comprising the stepsof: forming a first insulation film over a crystalline semiconductorfilm; patterning the first insulation film to form a gate insulationfilm over a portion of the crystalline semiconductor film; oxidizing asurface of the crystalline semiconductor film with an oxidizing watersolution to form an oxide film; forming a conductive film over the oxidefilm and the gate insulation film, the conductive film comprising asemiconductor film containing an impurity having one conductivity type;patterning the conductive film to form a gate electrode, a sourceelectrode, a drain electrode; and heating the crystalline semiconductorfilm, the oxide film, the gate insulation film, the gate electrode, thesource electrode, and the drain electrode.
 13. A manufacturing methodfor a field-effect transistor according to claim 12, wherein theimpurity contained in the source electrode and the impurity contained inthe drain electrode are dispersed to the crystalline semiconductor filmin heating the crystalline semiconductor film, the oxide film, the gateinsulation film, the gate electrode, the source electrode, and the drainelectrode.
 14. A manufacturing method for a field-effect transistoraccording to claim 12, wherein the oxidizing water solution is one ofozone water solution and hydrogen peroxide water solution.
 15. Amanufacturing method for a field-effect transistor according to claim12, wherein said one conductivity is an n-type conductivity.
 16. Amanufacturing method for a field-effect transistor according to claim12, wherein said one conductivity is a p-type conductivity.
 17. Amanufacturing method for a field-effect transistor according to claim12, wherein the crystalline semiconductor film, the oxide film, the gateinsulation film, the gate electrode, the source electrode, and the drainelectrode are heated in an inert gas ambient.